Following World War II the United States experienced power shortages, inflated electric rates and a shortage of equipment for cooling facilities. The principles for using an ice build up/ice melt cycle to cool buildings evolved during this time. Ice was built up at night when ambient temperatures were cooler. The ice would then be used to cool water which was circulated through the facility to be cooled during the day. This equipment, however, was frequently cumbersome, inefficient and hard to regulate.
During recent years the interest in thermal storage using the ice build up/ice melt cycle has substantially increased. The cost of electricity has soared for all users, encouraging energy conservation measures. At the same time, environmental restrictions have made the use of glycol type heat exchange fluids and fluorocarbon refrigerant gases correspondingly more expensive and highly regulated, favoring environmentally friendly, energy-saving techniques.
Electric utilities have also adopted usage and demand sensitive billing systems. In this rate structure, electricity rates are more expensive during the hottest hours of the day when the demand is greater than in the evening hours. In some cases, the highest daily usage period is used to determine the rate structure for the facility throughout the year, allowing the summer peak usage to inflate a facility's rate all year, not just during the summer.
These energy conservation trends encouraged exploration of innovative technology. Unfortunately, many problems were encountered in the practical utilization of "energy storage" technology via the ice build up/ice melt cycle for the modern-day air conditioning. Frequently, the ice melt patterns were spotty or uneven, giving ineffective water flow over the ice, resulting in inefficient cooling. This was a particularly troublesome problem during conditions of partial load. The water used to cool the facility would not be lowered to the required temperature, making the system inefficient.
In some systems, the ice would be formed around glycol-containing coils. Glycol was thus circulated through the coils to freeze ice at night and act as a coolant, melting the ice during the day. As the ice melt portion of the cycle proceeded, the ice would melt from the inside out, forming a layer of insulating water around the coil, decreasing the efficiency of the system. Additionally, the glycol coolant is expensive and can be hazardous.
Previous versions of this cooling technique utilized a water circulation equipment configuration that was often unreliable. Water to be recirculated throughout the facility being cooled must be kept free of particulate matter and agitated. Previous ice melt/ice build-up thermal storage devices used air agitation which led to cooling loss and maintenance problems. The heat from the air compressor and the ambient air used by air agitation systems melted the ice, leading to system inefficiency in addition to adding contaminants to the tank and requiring energy itself. Air agitation equipment frequently experienced maintenance problems in these prior art systems, resulting in unacceptable cooling losses. Refrigerant oil tended to escape the compressor system where it was needed for lubrication and compressor cooling and migrate to the cooling coils where it was deposited when the liquid refrigerant was expanded.
Thus, there exists a need in thermal storage technology for an improved apparatus making use of the ice build up/ice melt cycle. More specifically, a more efficient apparatus is needed having improved water circulation patterns over the ice, improved agitation in the ice tank, an improved oil recovery system and one that uses no hazardous materials.